Generally magneto-optical storage media consist of an amorphous magnetic alloy, or a polycrystalline alloy, with very small crystallite sizes. Generally, these storage media o contain a rare earth element and at least one transition metal. The storage media are applied in a vacuum to a carrier as a z thin recording layer. The storage of the information results from a thermal change in the magnetic structure of the media. The recording is accomplished by focusing a beam with a high energy density, preferably a laser beam, on the surface of the recording layer. The radiation energy from this beam heats the recording layer, in substantially point-shaped regions, to a temperature above the Curie temperature, T.sub.C, or a temperature above the magnetic compensation temperature, to form a pattern of magnetic zones with reversed polarity. After this heating, the plane of polarization of a laser beam with lower energy is rotated upon passage through the recording layer (Faraday effect) or reflection at the recording layer (Kerr effect). Stored information can be read from the recording layer by measuring this angle of rotation, or reflection, .theta..sub.K. The signal-to-noise ratio, or the carrier-to-noise ratio, C/N, is approximately proportional to the product of .theta..sub.k x.sqroot.R, where .theta..sub.K is the Kerr angle and R the reflection factor. With an increase of the Kerr angle .theta..sub.K, a correspondingly improved carrier-to-noise ratio, and an increased read-out, are obtained. In addition to a large Kerr angle and a good signal-to-noise ratio, the storage media should have a high coercivity, i.e., an approximately rectangular magnetization loop.
Generally, a multilayer magneto-optical medium contains two different materials, a ferromagnetic material such as cobalt, and a nonmagnetic material, such as copper. These materials are applied, alternating one after the other, as layers with different densities to a substrate. By changing the layer thickness, the wavelength of the maximum Kerr angle, .theta..sub.K, can be shifted In this multilayer system, also called an artificial superlattice, however, the Kerr angle .theta..sub.K, is always smaller than in an individual layer of the same ferromagnetic material. Multilayer systems such as described in this paragraph are generally discussed in "Journal of the Physical Society of Japan", (Vol. 55, No. 8, August 1986, pages 2539 to 2542), the teachings of which are hereby incorporated by reference.
An object of the invention is a magneto-optical storage medium with a large Kerr angle and high coercivity which makes possible a high data density and a high recording and readout rate.